The reforming of petroleum hydrocarbon streams is one of the important petroleum refining processes that may be employed to provide high-octane-number hydrocarbon blending components for gasoline. Although various reforming catalysts have been employed during the history of the reforming process, the preferred reforming catalyst is a catalyst containing a Group VIII noble metal, such as platinum. Recently, the preferred reforming catalysts are the bi-metallic an multi-metallic reforming catalysts which employ various combinations of hydrogenation metals, such as platinum-iridium, platinum-rhenium, platinum-gallium, and iridium-gold. Many of these bi-metallic and multi-metallic catalysts require sulfiding prior to their use for reforming in order to eliminate, or at least minimize, the excessive hydrocracking that occurs at the start of the reforming operation with a fresh catalyst or a regenerated catalyst.
Generally, the start-up procedure for a reforming process employing a platinum catalyst comprises heating the reactor to about 800.degree. F. in the presence of a circulating gas under pressure. This circulating gas can be either natural gas or a recycle gas from another reformer. Such recycle gas contains hydrogen and light hydrocarbons. In general, such gas may contain anywhere from 70 to 80 weight percent hydrogen. When the reactor temperature has reached 800.degree. F., the naphtha feedstock is introduced into the reaction zone and hydrogen is produced immediately.
When a bi-metallic or multi-metallic catalyst is employed, hydrocracking of the light hydrocarbons will occur during the heating-up period with the recycle gas and during the naphtha flow. It has been found that a sulfiding pretreatment of the catalyst will greatly reduce such initial excesive hydrocracking. Generally, sulfiding procedures require reduction of the catalyst with pure hydrogen at high temperatures, for example, 700.degree. F. or above, and then subsequent sulfiding with hydrogen sulfide or other sulfur compounds at such high temperature. The use of such pure hydrogen is expensive. Moreover, when the gas is circulated to heat the catalyst bed, the gas will pich up hydrocarbons from the liquid in the high-pressure separator being used in the system. These hydrocarbons will then be hydrocracked during the heating-up period that is conducted for the multi-metallic catalyst.
There has now been discovered a method for sulfiding a bi-metallic or multi-metallic catalyst when employing a hydrogen-rich gas containing light hydrocarbons. Such method may be used conveniently as the sulfiding pretreatment step in the start-up or initial operation of a reforming process unit employing a bi-metallic or a multi-metallic catalyst. Hence, there has also been discovered a method for initiating the reforming of a petroleum hydrocarbon stream in a reforming reaction zone containing a multi-metallic or bi-metallic catalyst, when a hydrogen-rich gas containing light hydrocarbons is used. These methods, although using impure hydrogen, eliminate, or at least minimize, the above-described difficulties.